Leakage from underground storage tanks have created many small pollution problems and some major disasters. Since fuels containing hydrocarbons flow into ground water aquifers, contamination of underground water supply can be serious and widespread. Hydrocarbon fuels contain substances which are extremely hazardous to wildlife and humans such as benzene. Clean up of spilled hydrocarbon liquids from the surrounding earth and ground water tends to be an extremely expensive proposition, far outweighing the cost of prevention.
Tanks for liquid storage such as gasoline, diesel fuel and other petroleum products have been constructed in various ways including composite construction from multiple materials including steel, fiberglass and plastics such as polyethylene. Many tanks are fabricated from steel which corrodes readily through contact with the surrounding earth and release of petroleum products into the ground is inevitable without cathodic protection. Fiberglass tanks, while resistant to corrosion are generally brittle and can be cracked through improper handling during shipping and also during backfilling operations. In view of the above problems, some solutions have been attempted which include providing a non-corroding covering for steel tanks. One example is shown in the U.S. Pat. No. 4,744,137. This encasing method includes wrapping a cylindrical tank with a plastic layer, welding the layer and then adding end caps to the tank and layer and welding on the end caps.
Federal Regulations have also required that leak detection be used in connection with underground storage tanks, and while several methods have been proscribed, that shown by U.S. Pat. No. 4,744,137 illustrates a common method which includes a pipe extending from an accessible location so that leaked fluid may be detected beneath the interior liner between the exterior shell. In order for the leak detection system to operate, interstitial spaces are provided to permit fuel leaking from the interior tank to flow to the bottom of the tank between the tank and the outer shell.
Generally, pumping components and piping ingress are located at the top of the tank. A leak containment sump-riser apparatus is generally joined to a manway at the top of the tank. Such a sump-riser assembly is shown, for example in U.S. Pat. No. 4,050,408. Attaching the sump riser apparatus to the manway generally includes connecting the sump-riser apparatus to the manway via a bolting flange on the manway and at the bottom end of the sump base.
In each of the prior assemblies, any time a mechanical connection is required, chance for leakage is present. In view of the foregoing, it can be seen that there is a need for a containment tank which eliminates the need for welded seams in the construction of the secondary containment layer and also eliminates unnecessary bolted connection between a manway and the sump-riser apparatus base.